The invention is based on a fuel injection pump and more particularly to an electrically controlled fuel injection pump for internal combustion engines.
In a fuel injection pump known from U.S. Pat. No. 4,459,963 to Gross et al, two pump pistons disposed side by side in a fuel injection pump housing are provided, each driven by a separate camshaft. Each of the pump pistons feeds into a separate single fuel injection line, associated with that piston, to a fuel injection valve of the associated internal combustion engine. The control of the injection quantity is effected via a common overflow conduit, which can be opened to a relief space by means of a magnetic valve. Also, the pump pistons execute their pumping strokes in alternation; to prevent the quantity of fuel pumped at high pressure by one pump piston from being able to flow out to the relief side during an intake or filling stroke of the other pump piston, a slide valve control is provided. The pump piston itself, with a control edge, acts as the valve slide. As an alternative, check valves are also provided, in the fuel fill line to the individual pump work chambers among other locations. The known fuel injection pump is thus designed as a kind of in-line injection pump, with each pump piston serving to supply fuel to one injection site.
In the embodiment according to the parent invention, the pump pistons are driven by a common cam, and the overflow conduit has conduit segments that begin in the pump work chambers and discharge in a guide bore of a rotationally driven distributor, embodied as a slide of a rotary slide valve, which has a recess via which, in the course of the distributor rotation, at least two of the segments of the overflow conduit of the pump piston executing a pumping stroke at that time communicate with one another. A part of the overflow conduit that extends onward from the recess communicates with a distributor opening on the distributor, by means of which pressure lines leading to the injection sites are made to communicate successively with the overflow conduit during the rotation of the distributor. An object of this invention is to obtain a fuel supply to a plurality of injection sites, and a plurality of pump pistons cooperate, to attain the high injection pressure for one injection site. In this way, with a compact fuel injection pump, a high pumping rate is attained, which is continuously available successively to each injection nozzle. In the central guide of a rotary slide valve of this type, it is possible to build up a desired injection pressure, and depending on the rotational position of the rotary slide valve, injection valves are acted upon by the pump pressure until such time as a corresponding speed regulation takes place, for instance by opening of an electrically controlled valve to a relief chamber. With the embodiment of the injection pump of the parent patent application filed Jan. 23, 1989, it was not readily possible to make a selection of the instant of injection for a preinjection independently of and without impairing a main injection.